1. Field of the Invention
The present invention relates to a hybrid vehicle having both an engine and a motor as power sources, and more specifically to a hybrid vehicle having a changeover mechanism that changes connection of the motor between a drive shaft linked with the wheels and an output shaft of the engine.
2. Description of the Related Art
A parallel hybrid vehicle is one type of the hybrid vehicles having both an engine and a motor as power sources. The parallel hybrid vehicle has a power regulation unit linked with the engine. Part of the power output from the engine is transmitted to a drive shaft linked with the wheels via the power regulation unit, while the residual power is regenerated as electric power. The regenerative electric power is accumulated in a battery or is used to drive the motor, which is used as the power source. The parallel hybrid vehicle controls the power regulation unit and the motor, so as to arbitrarily convert the revolving speed and the torque output from the engine to those suitable for the drive shaft. The hybrid vehicle selects a desirable driving point of the engine having a high driving efficiency and drives the engine at that point, irrespective of the revolving speed and the torque of the drive shaft, thus ensuring excellent resource saving effects and less emission.
In the parallel hybrid vehicle, the motor may be linked with either the drive shaft or the output shaft of the engine. When the motor is connected with the drive shaft, the engine, the power regulation unit, and the motor are linked in this order. FIG. 30 schematically illustrates the structure of a hybrid vehicle having a motor linked with a drive shaft. In the example of FIG. 30, a pair-rotor motor CM having an inner rotor IR and an outer rotor OR that are rotatable relative to each other is used as the power regulation unit. As illustrated in FIG. 30, the pair-rotor motor CM is connected to an output shaft CS of an engine EG, whereas an assist motor AM is linked with a drive shaft DS. This structure ensures the high driving efficiency in the state of underdrive when the revolving speed of the drive shaft DS is lower than that of the engine EG. This structure is called xe2x80x9cunderdrive connectionxe2x80x9d in this specification.
FIG. 31 shows power transmission in the underdrive connection when the revolving speed of the engine EG is higher than that of the drive shaft DS. The power output from the engine EG is reduced in revolving speed and enhanced in torque to be output from the drive shaft DS. The pair-rotor motor CM transmits a power PU1 output from the engine EG as a power PU2 of the reduced revolving speed. A slip occurs between two rotors in the pair-rotor motor CM, so that electric power is generated based on the slip. Part of the power PU1 is accordingly regenerated as an electric power EU1. The assist motor AM is driven with this regenerative electric power to increase the torque of the drive shaft DS. This generates a power PU3 corresponding to the required revolving speed and torque of the drive shaft DS.
FIG. 32 shows power transmission in the underdrive connection when the revolving speed of the engine EG is lower than that of the drive shaft DS. The pair-rotor motor CM carries out the power running to transmit the power PU1 output from the engine EG as a power PU4 of the raised revolving speed. The assist motor AM acts as a load to reduce its excess torque, thereby outputting the power PU3 corresponding to the required revolving speed and torque of the drive shaft DS. The assist motor AM regenerates part of the mechanical power PU4 as an electric power EU2, so as to apply the loading. This regenerative electric power is used for the power running of the pair-rotor motor CM.
In the case where the revolving speed of the engine EG is higher than that of the drive shaft DS (in the case of FIG. 31), the electric power regenerated by the pair-rotor motor CM located on the upstream side is supplied to the assist motor AM located on the downstream side in a path along which the power output from the engine EG is transmitted to the drive shaft DS. In the case where the revolving speed of the engine EG is lower than that of the drive shaft DS (in the case of FIG. 32), on the other hand, the electric power regenerated by the assist motor AM located on the downstream side is supplied to the pair-rotor motor CM located on the upstream side. The electric power supplied to the pair-rotor motor CM is subsequently supplied to the assist motor AM located on the downstream side as a mechanical power. This results in a circulation of power xcex31 as shown in FIG. 32. The circulation of power xcex31 reduces the effective power transmitted to the drive shaft DS out of the power output from the engine EG, thus lowering the driving efficiency of the hybrid vehicle.
When the motor is connected with the output shaft of the engine, on the other hand, the engine, the motor, and the power regulation unit are linked in this order. FIG. 33 schematically illustrates the structure of the hybrid vehicle having the motor linked with the output shaft of the engine. In the example of FIG. 33, the assist motor AM is linked with the output shaft CS of the engine EG, whereas the pair-rotor motor CM functioning as the power regulation unit is connected with the drive shaft DS. This structure ensures the high driving efficiency in the state of overdrive when the revolving speed of the drive shaft DS is higher than the revolving speed of the engine EG. This structure is called xe2x80x9coverdrive connectionxe2x80x9d in this specification.
FIG. 34 shows power transmission in the overdrive connection when the revolving speed of the engine EG is higher than that of the drive shaft DS. FIG. 35 shows power transmission in the overdrive connection when the revolving speed of the engine EG is lower than that of the drive shaft DS. Only the pair-rotor motor CM is capable of regulating the revolving speed of the transmitted power. The phenomena occurring in the overdrive connection are just opposite to those occurring in the underdrive connection. In the case where the revolving speed of the engine EG is higher than that of the drive shaft DS (in the case of FIG. 34), an electric power EO1 regenerated by the pair-rotor motor CM located on the downstream side is supplied to the assist motor AM located on the upstream side. In the case where the revolving speed of the engine EG is lower than that of the drive shaft DS (in the case of FIG. 35), on the other hand, an electric power EO2 regenerated by the assist motor AM located on the upstream side is supplied to the pair-rotor motor CM located on the downstream side. In the structure that the motor is linked with the output shaft of the engine, a circulation of power xcex32 occurs in the case of FIG. 34. This lowers the driving efficiency of the hybrid vehicle.
In the hybrid vehicle, a high efficiency driving area defined by the vehicle speed and the output torque depends upon the connection of the assist motor AM. One proposed technique changes the connection of the assist motor AM between the engine and the drive shaft, in order to improve the driving efficiency of the hybrid vehicle over a wide range.
A diversity of problems, however, arise in the process of changing the connection of the assist motor AM. A concrete example of the changeover mechanism is described here. FIG. 36 illustrates the structure of a hybrid vehicle in which the connection of the assist motor AM is changeable. The connection of the assist motor AM is changed by means of a synchronized gear unit including three gears SG1, SG2, and SG3. A rotor of the assist motor AM is linked with the gear SG3 that is slidable in the direction of the arrow. The gears SG1 and SG2 are respectively connected to the rotating shafts of the clutch motor CM and the engine EG. Sliding the gear SG3 as shown by the arrow enables the connection of the assist motor AM to be changed.
The synchronized gear unit requires a certain space, in which the gear SG3 is movable in the axial direction. This results in making the whole changeover system undesirably bulky. The size expansion of the changeover system is a significant problem especially on a vehicle, since the allowable space for mounting the power system is restricted in the vehicle. In the synchronized gear unit, the gear SG3 moves by a relatively long stroke between the gears SG2 and SG1 in the course of the changeover. The changeover accordingly requires a relatively long time. The changeover is implemented via a neutral state, in which the gear SG3 is coupled neither with the gear SG2 nor with the gear SG1. This causes a torque drop to instantaneously lower the power of the drive shaft.
The above description regards the structure using the synchronized gear unit. The same problem of making the whole changeover system undesirably bulky is also found in another structure using two clutches that are arranged in the axial direction to connect and disconnect the assist motor with and from the engine or the clutch motor. Another disadvantage of this structure is that the successive changeover of the two clutches requires a relative long time period.
The object of the present invention is thus to provide a hybrid vehicle, in which a changeover of connection of a motor is carried out with a small-sized changeover mechanism within a short time period.
At least part of the above and the other related objects is attained by a hybrid vehicle, which includes: an engine having an output shaft; a drive shaft from which driving power is output; a power regulation unit that is connected with both the output shaft and the drive shaft to vary power output from the engine through an input and an output of electric power and transmit the varying power to the drive shaft; a motor having a rotating shaft; and a changeover mechanism that changes connection of the rotating shaft of the motor between the output shaft and the drive shaft. The changeover mechanism is a dual clutch that includes a first clutch and a second clutch respectively arranged inside and outside the rotating shaft of the motor, the first clutch connecting and disconnecting the rotating shaft with and from the output shaft, the second clutch connecting and disconnecting the rotating shaft with and from the drive shaft.
The dual clutch ensures a space-saving layout of the rotating shaft, the output shaft, and the drive shaft and thereby reduces the size of the whole changeover system. The dual clutch includes two clutches aligned in the radial direction and has a greater dimension in the radial direction than that of a single clutch. The power system of the hybrid vehicle, however, has relatively large-sized constituents, that is, the motor, the power regulation unit, and the engine, arranged in the radial direction. The size expansion of the changeover mechanism in the radial direction accordingly does not lead to any significant expansion of the size of the whole changeover system. Application of the dual clutch, on the other hand, shortens the dimension in the axial direction, which gives a significant contribution to the size reduction of the whole changeover system.
The dual clutch also enables the connection of the motor to be changed quickly. This is because the changeover does not accompany a shift of any gear in the structure of the present invention, unlike the structure of FIG. 36 using the synchronized gear unit. The present invention implements the changeover not via the neutral state, thus effectively preventing a torque drop.
A variety of arrangements may be applicable to the dual clutch. Especially preferable is a dual clutch actuated by electromagnetic force. Regulation of the electromagnetic force enables the operations of the dual clutch to be controlled relatively easily with a high accuracy and a high response.
The dual clutch may be an electromagnetic roller clutch using rollers as coupling elements. The roller clutch that has a relatively small size but is able to transmit a relatively large power is desirably used for the changeover mechanism of the present invention. The dual clutch is, however, not restricted to the roller clutch, but may have a structure in which two clutch plates are attracted to and separated from each other by the function of electromagnetic force.
The connection of the motor may be changed manually.
It is, however, preferable that the hybrid vehicle of the present invention further includes: a decision unit that determines whether or not a changeover of connection of the motor is required, based on driving conditions of the hybrid vehicle and a current connecting state of the motor; and a changeover controller that controls the changeover mechanism to change the connection of the motor when the changeover is required.
This arrangement enables the connection of the motor to be changed adequately according to the driving conditions of the hybrid vehicle. For example, this arrangement changes the connection of the motor to prevent the circulation of power discussed previously with FIGS. 30 through 35. This preferably improves the driving efficiency of the hybrid vehicle.
The requirement of the changeover is determined in a variety of ways.
For example, the decision unit determines that the changeover of connection of the motor is required when an increment of a required torque to be output from the drive shaft is not less than a predetermined level while the motor is linked with the output shaft of the engine.
This corresponds to a changeover from the structure of FIG. 33 to the structure of FIG. 30 in response to an abrupt increase in required torque. As described previously, the structure of FIG. 33 ensures the high driving efficiency when the revolving speed of the engine is lower than that of the drive shaft. The structure of FIG. 30, on the other hand, ensures the high driving efficiency under the opposite condition. In the case of an abrupt increase in required torque, the driver generally desires abrupt acceleration. This raises the revolving speed of the drive shaft, and it is expected that the structure of FIG. 30 gives the higher driving efficiency. The hybrid vehicle of the above application thus carries out the changeover of connection of the motor to the structure of FIG. 30 in response to the abrupt increase in required torque.
The decision with regard to the requirement of the changeover advantageously ensures the quick acceleration, in addition to the improvement in driving efficiency. It is desirable that the motor outputs a torque in addition to the output of the engine in the course of acceleration. In the case where the motor is connected with the output shaft of the engine, the whole torque is output via the power regulation unit located on the downstream side. There is accordingly a fair possibility that the upper limit of the torque output from the drive shaft is restricted by the capability of torque transmission of the power regulation unit. In the case where the motor is connected with the drive shaft, on the other hand, a large torque can be output from the drive shaft without such limitations. This structure thus ensures a sufficient acceleration.
It is preferable that the changeover controller includes: a first controller that causes a released clutch between the first clutch and the second clutch to be coupled in an allowable range according to a difference between rotating states of two shafts linked with the released clutch, thus reducing the difference between the rotating states of the two shafts; and a second controller that causes a changeover to be carried out between the first clutch and the second clutch when it is determined that the rotating states of the two shafts satisfy a predetermined coupling condition with regard to the released clutch by the execution of the first controller.
In order to couple the released clutch, it is required to make the revolving speeds of the two shafts linked with the released clutch substantially coincident with each other. One possible method controls the power regulation unit and the other constituents linked with the two shafts to equalize the revolving speeds of the two shafts. The control technique adopted in the above arrangement causes the released clutch to be coupled in an allowable range of the clutch even when the two shafts have different rotating states, and gradually synchronizes the rotating states of the two shafts, at least one of their revolving speeds and the torques. This arrangement ensures the quick synchronization of the rotations of the two shafts and desirably shortens the time required for completion of the changeover. This control technique may be adopted alone or in combination with the control of the power regulation unit and the other constituents linked with the released clutch.
The released clutch can be coupled in the allowable range of the clutch in a variety of ways. In one embodiment, the released clutch is coupled with a higher coupling force against a decrease in revolving speed difference between the two shafts. In another embodiment the coupling force of the released clutch is varied in a stepwise manner. In still another embodiment the released clutch may be coupled while the coupling force of the released clutch is varied in a fluctuating manner.
The first and the second embodiment represent to the half coupled state. When the two shafts have a significant difference in revolving speed, the clutch is coupled with a small coupling force to cause a slip. The function of a frictional force acting between the two shafts causes the revolving speeds of the two shafts to be substantially coincident with each other. A gradual increase in coupling force with a decrease in revolving speed difference enables the revolving speeds to be synchronized quickly. In the second application, the coupling force may be varied by several steps until the rotating states of the two shafts satisfy the coupling condition. The coupling force to cause the slip may alternatively be kept until the rotating states of the two shafts satisfy the coupling condition. The second application of varying the coupling force in a stepwise manner advantageously facilitates the regulation of the clutch. This simplifies the circuit structure of the clutch that works by the function of electromagnetic force.
In the third embodiment, the coupling force may be varied according to the impact torque generated on the clutch in the coupling process. Coupling the clutch under the condition that the two shafts have significantly different rotating states causes a large impact torque to act due to the inertia. A decrease in coupling force reduces the torque applied to the clutch and effectively prevents the life of the clutch from being extremely shortened. The impact torque acting previously reduces the difference in rotating state between the two shafts. The arrangement of varying the coupling force of the clutch in a fluctuating manner also shortens the time required for completion of the changeover.
In accordance with preferred embodiment of the control procedure to shorten the time required for completion of the changeover, the changeover mechanism includes a roller clutch acting by the function of electromagnetic force and attains at least three different coupling states, that is, a released state, a fully coupled state to allow transmission of a torque via rollers, and a partly coupled state to allow transmission of a torque not via the rollers in a range lower than the torque transmittable in the fully coupled state. In this arrangement, the first controller causes the released clutch to gain coupling in the partly coupled state. The partly coupled state corresponds to a transient state, via which the clutch shifts from the released state to the coupled state.
It is also preferable that the first controller causes the roller clutch to be coupled in an intermittent manner. This arrangement requires simple binary regulation, that is, on-off regulation, of the electromagnetic force that drives the clutch, thus simplifying the control procedure.
Regardless of the execution or non-execution of the control procedure to shorten the time required for completion of the changeover, it is desirable that the changeover is implemented via a state in which both the first clutch and the second clutch are in a coupled state. This arrangement effectively prevents a torque drop in the course of the changeover and ensures a smooth drive of the hybrid vehicle.
In the hybrid vehicle of the present invention, a variety of structures are applicable to the power regulation unit.
For example, the power regulation unit includes a pair-rotor motor having a first rotor linked with the output shaft and a second rotor linked with the drive shaft.
The pair-rotor motor enables the power to be transmitted from one rotor to the other rotor through electromagnetic coupling of the two rotors. The pair-rotor motor also enables part of the power to be regenerated in the form of electric power by means of a relative slip between the two rotors. The pair-rotor motor having these two functions is desirably used as the power regulation unit.
In accordance with another preferable embodiment, the power regulation unit includes: a generator having a rotor shaft; and a planetary gear unit having three rotating shafts, which are respectively linked with the output shaft, the drive shaft, and the rotor shaft.
This arrangement enables the power produced by rotations of the output shaft to be distributed and transmitted to the drive shaft and the rotor shaft, based on the general actions of the planetary gear unit. Part of the power input into the output shaft is accordingly transmitted to the drive shaft, and the power distributed to the rotor shaft is regenerated as electric power by the generator. These two factors ensure the functions of the power regulation unit.